Telephone system.



A'. H. DYSON. TELEPHONE SYSTEM. APPLICATION FILED JAN. 20, 1902.

Patented May 25, 1909.

THE Manus Psrsns co4, wnsumarmy, n. n:4

- l,Unrrnnfsrirrns ALFRED iinYsoN,

y rvTo all 'whomfit may cri/:wem:

fj citizen ofthe United Uiy y No. 923,035.

OF CHICAGO, ILLINOIS, ASSIGNOR TO AMERICAN ELECTRIC TELEPHONE COMPANY,OF CHICAGO, ILLINOIS, A CORPORATION.

TELEPHONE SYSTEM.

Be itknown that I, ALFRED H. DYsoN, a

States, residing at Chicago, inthe county of Cook and State of Illinois,have invented a certain new and useful Improvement in Telephone Systems,of

which the following is a specification.

My invention relates to telephone systems I. iny general, but'moreparticularly to telephone l I() 7 connected by systems involving two ormore exchanges trunk lines, and especially to `the"supervisory orclearing out signals by which y the operators at the different exchangesare `advisedy that'the subscribers are4 through talking. Iny telephonesystems of this character it is the practice, for example,

to `connect ,two exchanges by means of a f trunk line, and to in this`way make it possible for asubscriber ofone exchange to com municateywith a subscriber of the other exchange.y The operator at the exchangereceiving the call 1s ordinarily termed the originating operator,y whilethe operator at the other exchange isgusually known as the trunkingoperator.7` i Wlhen a call is sent in to the 'originating operator, thelatter then 'communicates with the other exchange, stat ing the numberofthe subscriber called for. y f t' The trunking operator theninsertsthe plug fcalled subscriber, and at the same time the yorigmatlngoperator of the trunk cord ycircuit in the jack of the n is instructedto insert the plug ofthe cord circuit in the jack ofthe trunk linebetween the two exchanges. In this way' the calling subscriber isconnected up with the called subscriber, and when the lattery answersthe callthe two sub-stations are then in. circuit. f It is also thepractice to provide the exchangeswith clearing out or sov thattheoperator at supervisory signals,

yknow when the subeach exchange may scribers have 'finished theirconversation.

kkticularly relates,

yceiver byr light two f supervisoryClamps,

` Inthe system to which my invention parthe `hanging up of the rethecalled subscriber operates to one at the A`switchboard of the trunkingoperator, and

` the other at the switchboard of the originatingv operator at the otherexchange.

y In this lway both operators are advised that the called subscriber isthrough talking. The arrangement is also such that when the callingsubscriberhangs up the receiver, a super l fvisory lamp is lightedat theswitchboard of Specification of Letters Patent. n `Application filedJanuary 20, 1902. Serial No. 90,383.

Patented May 2 5, 1909.

the originating operator, and when the latter withdraws the plug fromthe ack of the trunk line7 a supervisory signal, preferably a lamp, isalso operated at the switchboard of the trunking operator. In this waythe trunking operator simply acts on the instru@ tions of theoriginating operator, and makes such connections and disconnections asare operator.

While, as stated, my invention relates generally to trunking telephonesystems, it relates more particularly to the clearing outV orsupervisory signals for the two exchanges, and especially to the circuitarrangement whereby the originating operator advises the trunkingoperator that the calling subscriber is through talking and has hung upthe re ceiver.

Generally stated, it is the object of my invention to provide a simpleand efficient circuit arrangement vfor operating and controlling theclearing out signals of a trunk line system of the complete metalliccircuit and double supervisory type.

A special object of my invention is to provide an improved trunking cordcircuit, con sisting preferably of but a single plug and cord.

A further object is to provide local circuits and an improvedarrangement of relays for operating the supervisory or clearing outsignals at the trunking exchange.

It is also an object of my'invention to avoid the use of objectionablegrounded circuits between the two exchanges'7 and to thereby render thesupervisory or clearing out signals between the two exchanges morecertain in their operation.

A further object of my invention is to provide an improved arrangementof relays and supervisory lamps in the single cord of a trunking cordcircuit.

In addition to these, it is also an object of my invention to providefeatures of improvement tending to increase the general efficiency, andto render a system of this character more serviceable and reliable inits operation. Y

To the foregoing and other useful ends, `my invention consists inmatters hereinafter set forth and claimed.

The accompanying drawing is a diagram `showing the usual or ordinarycord circuit called Yfor and signaled by the originatingcertain detailsand to serve as the calling for the originating operator, the trunlingcord circuit for the trunking operator at the other exchange, the twocord circuits being shown connected bythe trunk line between the ktwoexchanges, and the apparatus at the called station, together with thesubstation line and terminal apparatus, being shown connectedwith thecord circuit of the trunking operator.

As thus illustrated, the arrangement involves a sub-station having areceiver 1, a receiver hook 2, a bell 3, grounded at 4, and the twocontact points 5 and 6. 1t will be understood, however, that theapparatus thus located at the sub-station can be of any suitable form orcharacter, and that only such parts or instruments are shown as isnecessaryT to an understanding of the invention. The said sub-station isconnected by metallic line conductors 7 and 3 with the central stationor exchange. As shown in the drawing, this exchange is provided with amultiple` switchboard, and with. a suitable line or calling signal. Theswitchboard apparatus involves a conductor 9, forming mediu'ml ofelectrical connection between thel ground 10 and the contact 11, thelatter being normally in contact with the contact piece 13. Contactpieces 12, 13, 14, 15, 16

and 17 are also provided, the strips or contactpieces 13, 14 and 16being preferably movable and connected by insulation. The contact piece16 is adapted to be engaged by the armature 18 of the relay 19, when thelatter isvenergized by the insertion of the trunk cord circuit pluginthe jack of the switchboard. The coil of said relay is preferablyconnected by a conductor 20 with the battery 21,v thelatter beinggrounded at 22. From the pole of this battery a conductor 23 leads tothe coil of the relay 24, and from this relay the current passes throughconductor 25 to the contact piece 17, which is normally in contact withthe movable contact piece 16. This relay can be arranged or line signalfor the sub-station having the receiver 1. A conductor 26 connects therelay 19 with the jacks on the switchboard. The conductors 27, 28 and 30connect certain of the said contact pieceswith the said jacks, while theconductor 29 leads from one of said contact pieces through theresistance 31 to the ground at 32. The conductors 33, 34, 35 and 36serve as medium of electrical connection between the jacks. Asillustrated, the upper jack comprises the casing or testing ring contact37, the sleeve contact 33, and the tip contact 39. The contact piece isconnected with the tip contact strip 39 by insulation- 41. The contactpiece 40 is adapted to engage the contact point 42 when the plug isinserted, completing a circuit yfrom the battery 21 through the relay 19and the ground 22 and 43. The lower jack, which is shown in use, theplug of the trunliing cord circuit being inserted, coniprises the ground44 and contact 45, and the contact strips or springs 46, 47, 43 and 49.It will be seen that the jacks are similar in form and construction.

The plug which is inserted in the lower ack comprises the tip contactand the sleeve contact 51, connected respectively with the tip andsleeve strands 53 and 52 of the single cord with which the trunkingoperator is provided at the exchange. where the said jacks are located.This single cord comprises the springs 54 and 55 vof the ringing key,and the adjacent contacts 56, 57, 53 and 59, it being' observed that thesaid springs are normally.

in contact with contacts 56-and 53. Conductors 60 and 61 leadrespectively from the contact points 57 and 56, while conductors 62 and64 lead respectively from the contacts 59 and 58. There is also aconductor 63, a spring 65 of the ringing key, and adjacent contactpoints 66 and 67. The other spring 68 of the ringing key is arranged tocooperate with the contact points 69 and 70. ductor 71 connects thecontact point 70 with the ringing generator 72, which is adapted to ringthe bell 3 at the sub-station. The said generator is preferably groundedat 73. The conductors 74 and 75 connect the contact points 67 and 69with the springs 76 and 77 of the listening key. This listening key canbe provided with contact points 78 and 79, the latter connected by aconductor S0 and the coil S1 with the operators receiver or headtelephone 82. The conductor 33 connects this receiver to the contactpoint 73. The springs 76 and 77 are connected by conductors 34 and 85with 'the coils S6 and 87 of the differential relay B. preferablyprovided Awith a condenser S9, and a contact point.

A contact point 83, a conductor 90, and an armature 91 are associatedwith the said relay B. This armature is preferably normally point and isalso preferably grounded at 92. The conductor 93, the repeating coil 94,the battery 95, the repeating coil 96 and the conductor 97 are connectedup in series with the coils of said differential tery is preferablygrounded at 93. The said repeating coils 94 and 96 serve to ind ctivelyconnect the two parts of the single cord. In the other part of the cordcircuit the said repeating coils 94 and 96-are separated by a condenser99. A conductor 100 connects the repeating coil 96 with the conductor126 of the trunk linel between the two exchanges, while the conductors101, 103 and the coil of the relay 104 form a bridging connectionAacross this part of the cord circuit. The conductor 102 preferably leadsfrom the conductor 101 to an associated contact piece. This relay 104 isprovided `with an armature 105, which normally bears against a Contact Aconaway from the said contact 1* relay. The said bat- I The conductor 30is 1'5" L to the battery and the other to a relay. ycontact piece '114is preferably connected 106 can beconnectedfby a conductor 108 with ythesupervisory lainp or clearing out signal 109. A conductor 110 preferablyleads from said lamp or clearing out signal to an associatedcontactpiece, and this single cord for the trunking operator is also preferablykprovided with a second clearing out signal or supervisory lanip 111.yThe conductors 112 and 113 lead from this lanip 111, one leading Thewith the said conductor 102, while the contact piece 115 is grounded.rlhe contact piece 116 is connected with the conductor 110. K' Thecontact piece 117 is preferably connected to move the contact piece 115when engaged by the armature 118 of the relay 119. This relay. isconnected `in parallel with the lamp 111, the coil of the relay and thelamp being preferably of eqinl resistance. The

conductor 120 connects said relay with a battery, ywhile the conductor121 and the resistancey 122 `forni lnediurn of electrical con- `nectionbetween the contact piece 115 and the ground 123. Thebattery 124 isconrnected, as stated, with both the lainp 111 and the relay 119, and ispreferably grounded at 125.` The cord circuit thus provided serves asthek connecting nieans by which the trunking operator is enabled. toestablish communiand 130 of an ordinary jack.

"fc/ation between the sub-station and the other f exchange. 1t will beobserved that this cord kcircuit consists of but a single cord-that is nto say, there is but 'one plug, the other end of die cordy circuit beingconnected directly to the `conductors 126 and 1.27, constituting the`complete metallic hne connection between the two exchanges. f

"At the second exchange, or at the eX- change where the call is supposedto originate, 'the said trunlr'line terminals are connected'withthe tipand sleeve contacts 129 At this second i exchange thecord circuit isillustrated as of the usual forin and character, and 1s such as isordinarily employed in exchanges for conc .necting' up two subscribersof the saine eX- change. This cord circuit for the originating roperatoris provided with a plug having tip and sleeve contacts 131 and 132,connected krespectively with the tip and sleeve straijidsf133 and 134ofthe said cord circuit. `These strands lead preferably to the springs135"A and 136 of the ringing key.

A conf ductor-137 and a ringing generator 138,

"grounded, at 139 and connected by a cony,ductor '140' with a contactpoint 141, are preferably associated with said ringing key.

;, y1t will also be observed that contact points 142 143 and 144 areprovided, the latter being connected with the said conductor 137.

Thev operators listening circuit includes a coiiductor145, a kcondenser14.6, a'contact lain point 147, a spring 148 of the listening key, and aconductor 149 connecting this spring with the contact point 142. Theconductor 150 connects the other spring 151 of the listening key withthe contact point 143. The listening contact 152 and the conductor 153are connected with the receiver of the operators talking and listeningset, and the condenser 146 is connected by the coil 154 and theconductor 155 with the said operators receiver 156. The ground 157,together with the conductor 158 and the arniature 159 are associatedwith the differential relay C. This armature is normally away from therelay, and is arranged to close a supervisory lamp circuit by engagingthe contact point 160. Said relay is provided with the differentiallywound coils 161 and 163, the foriner connected with the spring 151 by aconductor 162. A like conductor 164 connects the relay coil 163 with thesaid spring 148 of the listening key. The y supervisory lainp orclearing out signal 165 is interposed between the conductors 166 and167, the latter being connected with the relay contact point 160. Therelay coil 163 is connected with a battery by a conductor 168, while thesaine battery is connected with the relay coil 161 by a conductor 169.

The repeating coils 170 and 1.71 are arranged C;

at each side of said battery. The conductor 172 and the ground 173 areconnected with the said battery, which is preferably coniposed of twoseparate batteries 174 and 175. This cord circuit is also provided witha second supervisory signal 176, it being observed that the systemthroughout is of the double supervisory character. This supervisory 176is connected by a conductor 177 with the battery 174. The said lainp isalso preferably connected by a conductor 178 with the contact point 179of the differential relay D. This relay D, it will be observed, isarranged inthe other hall' of the cord circuit, and is substantiallylike the relay C. The contact point 179 is arranged to coperate with thearmature 180 of said relay, said arinature being preferably grounded at181. are preferably connected with the two repeating coils by conductors184 and 185. As with the relay C, these coils 182 and 183 are connectedwith the tip and sleeve contacts 186 and 187 of the other plug. Thisplug having the tip and sleeve contacts 186 and 187, is adapted tocooperate with the jack of the calling subscriber in establishing coniinunication between the latter and the eX- change at which theoriginating operator is located. This jack, and in fact, all of theswitchboard apparatus at the terminal of the calling subscribers line,can be substantially identical with that shown at the terminal of theline running from the sub-station of the called subscriber. For thisreason, l

'system comprises the sub-station of a called have illustrated but onesub-station, and have shown only the .switchboard apparatus for thisstation.

Thus it will be seen that as illustrated the Subscriber, .theswitchboard apparatus at which the line lof the sub-station terminates,the single cord and cord circuits of the trunking'operator at the iirstexchange, and the cord circuit of the originating operator at theexchange Where the call is assumed to have originated. As stated, thetrunking cord circuit is shown connectedwith :the originating operatorscord circuit by means of the conductoi constituting what is commonlyknown as a Htrunk line. As shown, the calling and the called subscribersare assumed to be connected and carrying-on conversation. In such case,the relays 19 and 104 are-energized, While the differential relays B, Cand D, owing to their differential Winding, allow the voice and talkingcurrents to pass without being energized. lt is the disconnectingvapparatus and the circuit arrangement lfor the clearing out signals, towhich my invention particularly relates, and assumin(T that the twosubscribers are through talking, the operations are as follows: Then thecalled subscriber hangs up the receiver 1, a groundedline circuit isimmediately comi pleted from the ground 4 through the bell 3 and thecontact point 5 to the receiver hook orswitch 2, thence through the lineconductor S and the relay contact piece 13 to the adjacent contact piece12, thence through conductor 30 to the tip contact 47, from the latterthrough the plug tip 50 and the cord strand 53 to the key spring 55,thence through the contact 56 and the conductor 61 to the liey spring65, through contact 67 and conductor 74 to 1ey spring 76, thence throughy conductor S4 and relay coil 86 to conductor 97, through the latter andthe repeating coil 96 to battery 95, and thence to ground at 9S and backto the ground connection at The completion of this circuit serves toenergize relay B, and to draw the armature 91 into .contact Withthecontact point S3. The energizing ofthe differential relay B is, it willbe seen, due to the fact that the returning of the receiver to the hoolat the sub-station operates to open the sleeve side .of the circuit,thereby cutting out the coil S7, and in this Way permitting the coil 36,which is in the tip side of the circuit, to energize the relay Theenergizing of this relay operates to close the local circuit from theground 92 through the armature 91 to the contact 83, thence through theconductor 90 to the lamp 111, through the latter and the conductor 112to the battery 124, thence to the ground at 125and back to the ground at92. he closing of this local circuit operates to light the saidsupervisory lamp 111, thereby adelV vising the trunlring operator thatthe called l for lsubscriber has hung up the receiver atthe subestation.ith the relay 119 arranged in parallel With the said lamp 111, it Willalso be seen that a second local circuit is closed through the ground 92and the armature 91 to the contact point 88, thence through conductors90 and 113 to the relay 119, through the conductor 120 to the battery124, and thence to the ground at 125 and back to the ground connectionat 92. This shunting et' the current serves to energize the relay 119,which immediately draws up its armature 11.8. The said armature inmoving toward the core of the relay 119 engages the lower contact spring117, and causes both the latter and the contact spring 115 to moveupward and into engagement respectively with the contacts 116 and 114.The shifting of these contact pieces operates to close a groundedtrunling line circuit from the ground 123 through the resistance 122 andthe conductor 121. to the contact piece 115, thence through contact 114and conductors 162 and 101 to the conductor 100, through the latter tothe conductor 126 of the trunking line, through the tip contact 129 ofthe jack at the originating exchange, thence through the plug tip 131and the cord strand 133 to the lrey spring 135, through contact point143 and conductor 150 to conductor 162, thence through the coil 161 andthe dillerential relay C, through conductor 169 and the repeating coil170 to the battery 175, thence through conductor 172 to ground at 173,and back through ground to the ground connection at 123. The circuitthus established through the ground and part of the trunlring line isenergized by the battery 17 5, and as the coil 161. of the di'lierentialrelay C is included in this circuit, it is therefore apparent that thelatter will be energized and Yill attract its armature 159. Thisarmature when attracted engages the contact point 160, therebycompleting a local circuit from the ground 157 through the conductor 15Sto the armature 159, thence through Contact point 166 and conductor 167to the supervi-L sory lamp 165, through this lamp and the conductor 166to the battery 175, thence through conductor 172 to the ground at 173,and thence back to the ground at 157. This, it will be seen., operatesto light the lamp 165, so as to advise the originating operator at theexchange of the calling subscriber that the called for subscriber isthrough talking and has hung up the receiver. Thus it Will be seen thatthe act of the called subscriber in hanging up the receiver operates tolight both the lamps 1.11. and 165, and to consequently indicate to boththe trunking operator and the originating operator that a disconnectionmay be made as soon as the callmg subscriber is through and sends in asignal to that eiect. The trunling operator, however, pays no attentionto this signal, and

ydoes ynot'remove the plug of the trunking cord circuitfrom the jackuntil a disconnectv ing signal is received from the originating operatorat the other exchange.

- yVVhenthe calling subscriber is through and i hangs kup'the receiver,-a grounded line circuit is completed through the supervisory ylamp 176,and the originating operator seeing f y this signalunderstands that thesubscriber at the sub-station from whence the calling kfcame'is throughand ready to be discono f 'nected The originating `operator thenwithl"drawstheplug of the cord circuit from the gized circuit in whichthe re jack having the tip and sleeve contacts 129 and 180, and this acton the part of the originating operator breaks or o )ens the eneray 104is ini y eluded.y LThis relay -104is, itwill be observed,

n battery y1 7 5 seQuently,

j i operator withdraws the plug from the trunking line jack,

this relay 104 is deenergized, and its armature 105 is allowed to fallback Tinto contact with the contact point 106. y This operates tocomplete a local circuit f from the ground 107 through the armature lamp109 and the conductor 110 to the con- 105 and the contact pointy 106 tothe 'conductor 108,'thence through the supervisory V tact pointll,through the contact spring f causes thecurrent from battery i theysupervisory [,117 and the contact 128 to the battery 124, thence to theground at 125 and back to the ground connection107. 5 This, it will beseen, 124 to light lamp ,109 through a short local circuit. This lampwhen lighted indil cates that the calling subscriber has signaled fora'disconnection, and thatthe originating operator has withdrawn the cordplug from line from the trunkinffcord circuit.

the trunking yline jack. The trunking operatoracting on this signalfromthe originating operator, withdraws ythe plug of the ksingle trunkingcord from the jack, having the tip and sleeve contacts 47 and 48, and 1nthis way disconnects the called subscribers Thus in disconnecting, the`called subscriber can signal boththe trunking operator and theoriginating operator atthe two exchanges, and

, the originating operatory is permitted to com- Y lamps.

pletely supervise and control the disconnecting, and to indicate to thetrunking operator the time at which it is proper for the latter to makethe final disconnection.

f. It will be seen thatthe cord circuit for the trunking operator,althoughconsisting of but a single cord and plug, is advantageously anddesirably providedwith two supervisory One of these lamps serves as aclearing out signaller a subscriber, while the t be observed that bothlamps are other lamp serves asa clearing out signal for the operator .atthe other exchange. It will lighted by comparatively short localcircuits. lt will also be observed that the local circuit for the lamp109 is preferably provided with two switch points, one normally closedby the relay 104, and the other held normally open by the relay 119.While the subscribers are talking, the normally closed switch pointyisheld open by the relay 104, which latter is under the control ol' theoriginating operator at the other exchange. It is' only when thesubscriber hangs up the receiver 1 that the relay 119 is operated, so asto close the normally open switch point. lt will also be seen that thisrelay 119 is energized by and included in a comparatively short localcircuit, and that in this way there is no necessity of providingobjectionable grounded circuits between the two exchanges -for causingthe operation of the lamp 109. This lamp is simply brought intooperation by the breaking or opening of the trunk line circuit, so as torelease the relay armature 105. The arrangement also affords opportunityfor an advantageous and effective use ol a differential relay in asingle cord trunk circuit. As a further advantage, the circuitarrangement enables the originating operator to know when the calledsubscriber answers the call. ln establishing connection between the twosubscribers, the lamp 165 continues to glow or burn until the calledsubscriber answers the call. lt will be seen, therefore, that with theforegoing combination of relays and circuits, a complete andsatisfactory supervision of the entire trunking system is afforded bothoperators, and that at the saine time the arrangement is simple andthoroughly eflicient. Furthermore, no objectionable grounded or othercircuit connections are employed, the certainty and efliciency of thesystem being particularly insured by the local circuit arrangement foroperating the supervisory lamps in the cord circuit of' the trunkingoperator. ln addition, the arrangement does not preclude the use of acomplete metallic talking circuit.

That 1 claim as my invention is:

1. ln a telephone system, the combination of sub-stations, exchangeshaving suitable line connection with said sub-stations, a trunk linebetween said exchanges, an operators cord circuit at one exchange, atrunking operators cord circuit at the other exchange, a supervisorysignal associated with the said cord circuit of the trunking operator, alocal circuit for operating said supervisory signal, a source of currentsupply included in said local circuit, a relay associated with saidlocal circuit and adapted to hold the latter open while the subscribersare talking, a source of current supply associated with said operatorscord circuit, and a trunk line circuit including said relay and saidsource of' current supply, said trunk line circuit being broken and thesaid local cause the operation lamp circuit at onepoin't, a

pervisory lamp lighted ators cord circuit at cuit open when thesubscribers operators cord circuit vis disconnected from.

the'trunkline, and the denergization oi said relay operating to closesaid local ciicuit and ol' said supervisory signal.`

2; In a ti'unking telephone system, the combination of a single cord andplug for the trunking operator, two supervisory lamps 1D" associatedwith said single cord, vsuitable local circuits and a source of currentsupply for operatingsaid supervisory lamps, and a differential relay forcontrolling they iiow of current through one lamp, and a plurality ofre- 1` lays for contiolling the ilow of current through the Votlieilamp.

3; In a trunking telephone system, the combination of a single cord andplug for the trunking operator, a double cord for the 20. originatingoperator, a trunk line between the two operators, a supervisory lampassociated with the said single cord, a source ol'l current supply and acircuit for lighting said lamp, a relay and circuit for closing saidrelay and a source `oi current supply and a suitable ciicuit for holdingsaid lamp circuit open-at another point while the subscribers aretalking, the said lamp circuit being closed and the suwhen the saiddouble cord for the originating operator is disconnected from the trunkline.

4. In a trunking system, the combination of two sub-stations, twoexchanges, coin- 35 plete metallic line connection between each exchangeand its allotted sub-station, coinplete metallic line connection betweensaid exchanges, a trunking operators .cord circuit at one exchange, anoriginating operthe other exchange, a supervisory lamp associated withsaid trunking operators cord circuit, a local circuit including saidsupervisory lamp, a relay adapted to be energized and to hold said localcirare talking, a source of current supply in the oiigiiiatiiigoperators cord circuit for energizing said relay,- a second supervisorylampl associated witli'said trunking operators cord circuit, a

local circuit and a source ot' current supply for lighting said secondsupervisory lamp,`

and a diiierential relay foi' controlling the operation of said secondsupervisory lamp.

5. In a trunking telephone system, a

trunkingoperators cord circuit, a supervisory lamp associated with saidcord circuit, a local circuit and a source of current supply forlighting said lamp, a shunt around said lamp, Va relay located in saidshunt, a second super- 6 OV visory lamp and a localcircuit for lightingthe same, the local circuit of said second supervisory lamp being openat two points while the subscribers are talking, an armature and contactpieces for closing said local circuit at one point, said armature beingassociated with and operated by said relay, and a switch forautomatically closing said local circuit at said other open point.

6. In a trunking telephone system, a trunking operators cord circuit, alocal circuit iovided with two switch points, relays for c osing saidswitch points, a supervisory lamp and a source of current supplyincluded in said local circuit, a trunkline connected with one of saidrelays, and a sub-station line and a suitable relay for controlling theoperation of the other of said relays.

7. In a trunking telephone system the combination of a single cord andplug for the trunking operator, a switchboard having jacks associatedwith said single cord,a substation having suitable line connection withsaid switchboard, a trunk line permanently connected vwith said singlecord, two supervisory lamps associated withsaid single cord, localcircuits and suitable sources ol current supply for lighting said lamps,two relays for controlling two switch points in one of said localcircuits, and a diii'erentially wound relay for controlling a switchpoint in another of said. local circuits.

8. In a trunking telephone system the combination of a trunkingoperators cord circuit, a trunk line permanently connected withsaidtrunking operators cord circuit, an originating operators cord circuit,a suitable plug and jack for establishing connection between said trunk`line and said originating operators cord circuit, supervisory lampsassociated with'l said originating operators coid circuit, localcircuits and la suitable source of current supply for lighting saidlamps, diiierentially wound relays for closing said local circuits, aswitchboard associated with said trunking operators cord circuit, av

sub-station having suitable line'connection with said switchboard, aswitchboard asso-A ciated withsaid originating operators cord circuit, asub-station having suitable line connection with said last mentionedswitchboard, supervisory lamps associated with said trunking operatorscord circuit, a differential relay and a local circuit and a source ofcurrent supply for causing the lighting of one of said lamps inthetrunking operators cord circuit, and a pair of relays and a local'circuit, together with a suitable source of current supply forcontrolling the lighting of the otherof said supervisory lamps for thetrunking operator.

9. In a telephone systeinthe combination of sub-stations and a centralstation and line connection between the same, a cord circuit located atsaid central station, a supervisory lamp and a suitable source ofcurrent supply associated with saidcord circuit, ashunt eX- tendingIaround said lamp, al relay in said shunt, and a signal circuit having aswitch point controlled by said relay, together with a supervisory relayfor controlling a norm ally f l'ellt Supply; f lay in said shunt, saidrelay having the same y trollingvsaid diiierential relay over "openSwitchpoint in the circuit of said lamp and relay.'

10. ln a telephone system, a cord circuit, a lampsignal associated-withsaid cord circuit and adapted yfor indicating the condition of a line, asource of current supply, a local circuit including said lamp signaland. source of our* a shunt around said lamp, a re- Aresistance ask saidlamp signal, a supervisory larnp for indicating thecondition of anotherline and a local circuit for operating the same, the local circuit forsaid supervisory lamp being yprovided with a switch point, and saidrelay being provided with an armature for opening and closing saidswitch point.

1 1, ln a telephone exchange system, the

' combination kol" a trunk line, a talking circuit including said trunkline, a differential relay in the talking circuit, the windings of saidrelay neutralizing each other when thus connectediny series, a suitablerelayi'or conthe trunk line, suitable circuit connections controlled bysaid differential relay, and a third relay 'cooperating with saidsuitable relay to control the said diferential relay.

i k12. yln a telephone exchange system, the combination of a trunk line,a talking circuit including said trunk line, a diiiierential relay inthe talking circuit, the windings of said rec lay neutralizing eachother when thus connected in series, a suitable relay for controllingsaid diiiierential relay over the trunk line, suitablecircuitxconnections controlled by said differential relay, adifferentially woundelectro-magnet having its neutralizing coils bridgedin series across the talking circuit, and means by which said electrolmagnet cooperates with said suitable relay to control said differentialrelay. l 13. ln a telephone exchange system, the l combination of atrunk line, a talking circuit l including said trunk line, adifferential relay l in the talking circuit, the windings of said re layneutralizing each other when thus conl nected in series, a suitablerelay for controlling said differential relay over the trunk l line,suitable circuit connections controlled by said differential relay, anda third relay cooperating with said suitable relay to control the saiddifferential relay, and common l batteries for `feeding talking currentthrough the differential coils to said circuit.

111. In a telephone exchange system, the combination of a trunk line, atalking circuit including said trunk line, a differential relay in thetalking circuit, the windings of said relay neutralizing each other whenthus connected in series, a suitable relay for controlling saiddi'liierential relay over the trunk l line, suitable circuit connectionscontrolled by said diiierential relay, a differentially woundelectro-magnet having its neutralizing cuit, and means by which saidelectro-mag net cooperates with said suitable relay to control saiddifferential relay, and common batteries for feeding talking currentthrough the differential coils to said circuit.

Signed by me at ,Chicago, Cook county, Illinois, this 16th day ofJanuary, 1902. i ALFRED H. DYSON.

Vitnesses:

ARTHUR F. DURAND, HARRY l. BAUMGARTNRR.

` coils bridged in series across the talking cir- 1 i l l l

